1. Field of the Invention
The present invention relates to a fluorescent lamp controller that is used in a copying machine or a facsimile apparatus, and to an original-document exposing apparatus having the foregoing controller.
2. Related Background Art
A fluorescent lamp has been used in a copying machine and a facsimile apparatus to expose an original document to light. The facsimile apparatus in an apparatus of the foregoing type must be able to repeatedly turn on and off. Furthermore, the fluorescent lamp must be able to quickly and stably turn on with an appropriate quantity of light to which the original document is to be exposed. Therefore, preheating of the fluorescent lamp has been performed in general.
If voltage is, at the time of turning the fluorescent lamp on, applied between two filaments before the filaments are not heated satisfactorily, the fluorescent lamp cannot easily be turned on, and the fluorescent lamp will be damaged. Accordingly, no voltage is applied between the two filaments for a predetermined period at the time of turning the fluorescent lamp on, but each of the two filaments of the fluorescent lamp is applied with voltage to be previously heated. After each filament has been heated satisfactorily, voltage is applied between the two filaments in accordance with the detected quantity of light to turn on the fluorescent lamp.
Furthermore, duty control has been employed with which the turning-on duty of the voltage to be applied between the filaments is adjusted to approach an aimed quantity of light. During the period in which the turning-on duty is turned on, applying of the voltage to each of the filaments is inhibited to prevent the filaments being heated excessively due to the heat of the filaments generated by a lamp electric current flowing between the two filaments, thereby preventing further heating of the filaments. During the period in which the turning-on duty is turned off, each filament is applied with voltage to heat the filaments in order to prevent cooling of the filaments.
However, with the foregoing conventional technology, the detected light quantity before the fluorescent lamp is turned on is a quantity detected in a state where no light quantity is present. Therefore, the turning-on duty is made to be 100% to quickly turn on the fluorescent lamp until the fluorescent lamp emits light with an aimed light quantity. That is, the period, in which the duty is turned off, is not present. However, applying of preheating voltage to each of the filaments is inhibited in the period in which the turning-on duty is turned on. Since the lamp electric current does not pass in a large quantity between the filaments, the filaments are gradually cooled as the time passes. If the lamp electric current passes in a sufficient quantity before the filaments are cooled, the filaments can be heated satisfactorily. If a long time takes for the lamp electric current to pass, the filaments are cooled, and therefore the fluorescent lamp cannot easily be turned on with an appropriate light quantity. Even if the fluorescent lamp is turned on, the filaments will be damaged.
Therefore, the conventional apparatus for exposing an original document to light encounters a problem in that exposure of an original document to light with an appropriate light quantity cannot quickly be started, and another problem in that exposure of an original document to light with an appropriate quantity cannot stably be performed.